Laboratory Selection for Beet Armyworm (Lepidoptera: Noctuidae) Resistance to Methoxyfenozide

Jeffrey Gore, John J. Adamczyk Jr.


Beet armyworms, Spodoptera exigua (Hübner), were artificially selected in the laboratory for resistance to the insect growth regulator, methoxyfenozide. A field collected beet armyworm colony was separated into three cohorts that were independently selected with three concentrations (0.033 ppm, 0.064 ppm, and 0.125 ppm) of methoxyfenozide incorporated into a meridic diet. These concentrations corresponded closely with the LC10 (0.033 ppm), LC50 (0.072 ppm), and LC90 (0.161 ppm), respectively, for the original colony. After seven generations of continuous exposure to methoxyfenozide, resistance in the colony selected at the low concentration did not increase significantly. In contrast, LC50 values increased 9.7- and 9.4-fold for the colonies selected at the moderate and high concentrations, respectively, over that of the original colony. Crosses between resistant and susceptible individuals indicated that the resistance was heritable. At 4 d after exposure, mortality of offspring from the reciprocal crosses was intermediate between mortality for the offspring from the parental crosses. When rated at 10 d, mortality of offspring from the reciprocal crosses was not different significantly from offspring from the cross between susceptible parents. These data will be important for developing a management program for beet armyworm resistance to methoxyfenozide.

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